1. Field of the Invention
This invention resides in the field of chemical processes for the treatment of crude oil fractions and the various types of products derived and obtained from these sources. In particular, this invention addresses reformation processes as ring-opening reactions and the saturation of double bonds, to upgrade fossil fuels and convert organic products to forms that will improve their performance and expand their utility. This invention also resides in the removal of sulfur-containing compounds, nitrogen-containing compounds, and other undesirable components from petroleum and petroleum-based fuels.
2. Description of the Prior Art
Fossil fuels are the largest and most widely used source of power in the world, offering high efficiency, proven performance, and relatively low prices. There are many different types of fossil fuels, ranging from petroleum fractions to coal, tar sands, and shale oil, with uses ranging from consumer uses such as automotive engines and home heating to commercial uses such as boilers, furnaces, smelting units, and power plants.
Fossil fuels and other crude oil fractions and products derived from natural sources contain a vast array of hydrocarbons differing widely in molecular weight, boiling and melting points, reactivity, and ease of processing. Many industrial processes have been developed to upgrade these materials by removing, diluting, or converting the heavier components or those that tend to polymerize or otherwise solidify, notably the olefins, aromatics, and fused-ring compounds such as naphthalenes, indanes and indenes, anthracenes, and phenanthracenes. A common means of effecting the conversion of these compounds is saturation by hydrogenation across double bonds.
For fossil fuels in particular, a growing concern is the need to remove sulfur compounds. Sulfur from sulfur compounds causes corrosion in pipeline, pumping, and refining equipment, the poisoning of catalysts used in the refining and combustion of fossil fuels, and the premature failure of combustion engines. Sulfur poisons the catalytic converters used in diesel-powered trucks and buses to control the emissions of oxides of nitrogen (NOx). Sulfur also causes an increase in particulate (soot) emissions from trucks and buses by degrading the soot traps used on these vehicles. The burning of sulfur-containing fuel produces sulfur dioxide which enters the atmosphere as acid rain, inflicting harm on agriculture and wildlife, and causing hazards to human health.
The Clean Air Act of 1964 and its various amendments have imposed sulfur emission standards that are difficult and expensive to meet. Pursuant to the Act, the United States Environmental Protection Agency has set an upper limit of 15 parts per million by weight (ppmw) on the sulfur content of diesel fuel, effective in mid-2006. This is a severe reduction from the standard of 500 ppmw in effect in the year 2000. For reformulated gasoline, the standard of 300 ppmw in the year 2000 has been lowered to 30 ppmw, effective Jan. 1, 2004. Similar changes have been enacted in the European Union, which will enforce a limit of 50 ppmw sulfur for both gasoline and diesel fuel in the year 2005. The treatment of fuels to achieve sulfur emissions low enough to meet these requirements is difficult and expensive, and the increase in fuel prices that this causes will have a major influence on the world economy.
The principal method of fossil fuel desulfurization in the prior art is hydrodesulfurization, i.e., the reaction between the fossil fuel and hydrogen gas at elevated temperature and pressure in the presence of a catalyst. This causes the reduction of organic sulfur to gaseous H2S, which is then oxidized to elemental sulfur by the Claus process. A considerable amount of unreacted H2S remains however, with its attendant health hazards. A further limitation of hydrodesulfurization is that it is not equally effective in removing all sulfur-bearing compounds. Mercaptans, thioethers, and disulfides, for example, are easily broken down and removed by the process, while aromatic sulfur compounds, cyclic sulfur compounds, and condensed multicyclic sulfur compounds are less responsive to the process. Thiophene, benzothiophene, dibenzothiophene, other condensed-ring thiophenes, and substituted versions of these compounds, which account for as much as 40% of the total sulfur content of crude oils from the Middle East and 70% of the sulfur content of West Texas crude oil, are particularly refractory to hydrodesulfurization.
In light of the deficiencies associated with hydrodesulfurization, new processes have emerged, the most notable being oxidative desulfurization, that seek to effectuate sulfur removal with greater efficiency. Essentially, such process involves oxidizing sulfur species that may be present, typically through the use of an oxidizing agent, such as a hydroperoxide or peracid, to thus convert the sulfur compounds to sulfones. To facilitate such oxidative reaction, ultrasound may be applied as per the teachings of U.S. Pat. No. 6,402,939 issued to Yen et al., entitled OXIDATIVE DESULFURIZATION OF FOSSIL FUELS WITH ULTRASOUND; and U.S. Pat. No. 6,500,219 issued to Gunnerman, entitled CONTINUOUS PROCESS FOR OXIDATIVE DESULFURIZATION OF FOSSIL FUELS WITH ULTRASOUND AND PRODUCTS THEREOF, the teachings of each are expressly incorporated herein by reference.
Advantageously, oxidative desulfurization can be performed under mild temperatures and pressures, and further typically does not require hydrogen. Additionally advantageous is the fact that oxidative desulfurization requires much less in terms of capital expenditures to implement. In this respect, oxidative desulfurization can be selectively deployed to treat only a single fraction of refined petroleum, such as diesel, and can be readily integrated as a finishing process into existing refinery facilities. Perhaps most advantageous is the fact that oxidative desulfurization can substantially eliminate all sulfur species present in a given amount of crude oil such that ultra-low sulfur levels can be attained, and in particular the lower standards being set forth in various legislative requirements regarding sulfur content levels.
Despite such advantages, however, oxidative desulfurization is presently ineffectual for use in large scale refining operations insofar as currently deployed oxidative desulfurization techniques only partially oxidize the sulfur species present to sulfoxides, as opposed to sulfones. In this regard, present oxidative desulfurization techniques are too ineffectual and cannot achieve sufficient oxidation necessary to implement on a large scale basis. Moreover, to the extent the sulfur species is only partially oxidized (i.e., to sulfoxide), eventual removal of the sulfur species, which is typically accomplished either through solvent extraction or absorption based upon the differential polarity of the sulfones assumed to be present through such process, fails to facilitate the removal of the sulfoxide components based upon its lesser degree of polarity (i.e., as compared to sulfones). Accordingly, substantial refinements to oxidative desulfurization must be made before such technology can be practically implemented.
In addition to sulfur-bearing compounds, nitrogen-bearing compounds are also sought to be removed from fossil fuels since these compounds tend to poison the acidic components of the hydrocracking catalysts used in the refinery. The removal of nitrogen-bearing compounds is achieved by hydrodenitrogenation, which is a hydrogen treatment performed in the presence of metal sulfide catalysts. Both hydrodesulfurization and hydrodenitrogenation require expensive catalysts as well as high temperatures (typically 400° F. to 850° F., which is equivalent to 204° C. to 254° C.) and pressures (typically 50 psi to 3,500 psi). These processes further require a source of hydrogen or an on-site hydrogen production unit, which entails high capital expenditures and operating costs. In both of these processes, there is also a risk of hydrogen leaking from the reactor.
As such, there exists a substantial need in the art for systems and methods that are operative to effectuate the removal of sulfur from refined fossil fuels that is substantially effective in removing virtually all of the sulfur species present in the fossil fuel that is further extremely cost effective and can be readily integrated into conventional oil refining processes. There is likewise a need in the art for such a method that is effective in removing nitrogen-containing compounds that is further cost-effective and substantially effective in removing virtually all of the nitrogen species present in such fossil fuel. Still further, there is a need for such a process that is capable of enhancing the quality of the refined fossil fuel treated thereby and that can be readily utilized in either large scale or small scale refinery operations.